Use of Ethyl (E,Z)-2,4-decadienoate in Codling Moth Management: Stimulation of Oviposition

Journal of the Entomological Society of British Columbia, Dec 2004 by Knight, A L, Light, D M

ABSTRACT

The effect of the pear volatile, ethyl (E,Z)-2,4-decadienoate (Et-E,Z-DD), on oviposition by codling moth, Cydia pomonella (L.), was evaluated in a series of choice and no-choice laboratory experiments and in subsequent field tests conducted in apple and walnut. Gray halobutyl elastomer septa loaded with 1.0 and 100.0 µg Et-E,Z-DD significantly increased the numbers of eggs laid by a laboratory population in 96 h no-choice assays by 2-fold. In addition, the number of eggs laid near the Et-E,Z-DD versus a solvent blank dispenser was significantly higher in choice bioassays across a similar range of septa loadings. Oviposition rates by a field-collected post-diapause strain of codling moth were significantly increased by the addition of a 1.0-µg septa versus a solvent blank dispenser in a no-choice bioassay. Field trials were conducted in apple and walnut to develop an artificial egg trap baited with Et-E,Z-DD to monitor codling moth oviposition. Septa loaded with 0.1 to 10.0 mg did not significantly increase oviposition versus solvent blank dispensers on a Mylar plastic collar trap or on the adjacent leaves and fruit in apple. Significantly more eggs were laid on the fruit and foliage than on the plastic collar. No eggs were deposited on non-bearing apple shoots baited with 0.1 - 40.0 mg Et-E,Z-DD septa. Similarly, no eggs were deposited on cylindrical wax paper-covered plastic traps baited with 10.0 µg to 1.0 mg Et-E,Z-DD septa in walnut orchards. The potential of Et-E,Z-DD to monitor codling moth's oviposition in the field, stimulate oviposition by field-collected strains under laboratory conditions, and to improve pest control by disrupting host location are discussed.

Key Words: Cydia pomonella, oviposition, kairomone, phenology, egg trap

INTRODUCTION

Codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) is typically monitored in fruit and nut orchards with sex pheromone-baited traps. The numbers and timing of male moths captured in these traps is used to infer the density of female moths and timing of oviposition (Riedl and Croft 1974, Riedl et al. 1976). The development of an effective, inexpensive tool to directly monitor the density of codling moth females and/or oviposition could improve its management. The sesquiterpene, (E,E)-α-farnesene (E,E-αF), a major constituent of apple fruit and leaf odors, was identified as a key adult and larval attractant for codling moth (Sutherland et al. 1974) and was shown to stimulate oviposition in both choice and no-choice laboratory bioassays (Wearing and Hutchins 1973). Unfortunately, E,E-αF is unstable in the presence of oxygen and has a very short residual activity (Anet 1969). Field trials evaluating the stimulatory effect of E,E-αF on codling moth oviposition have not been reported.

Direct monitoring of codling moth egg density in orchards through foliage and fruit sampling is labor intensive and often ineffective due to the relatively low population density of this pest in commercial orchards (Elkins 2002). A novel approach to monitor codling moth egg density in California pear orchards has recently been reported that uses the artificially cutting or damaging of fruit (Zoller and Zoller 2001). Pear clusters containing one cut-fruit (2.03.0 cm wedge cut 0.5-1.0 cm deep) were 95-times more likely to contain a codling moth egg than normal fruit clusters. Yet, a number of factors increase the variability of this approach including cultivar and days before harvest, i.e., Bosc pear clusters were more attractive than Bartlett; and the attractiveness of cut- versus uncut-fruit was only significantly different during the month before harvest (Zoller 2001). Unfortunately, the incidence of eggs among the cut-fruit cluster samples in commercial pear orchards was low (

Light et al. (2001) and Knight and Light (2001) found that ethyl (E,Z)-2,4-decadienoate (Et-E,Z-DD), a principal odorant from ripe pear (Jennings et al 1964), was a potent adult and larval kairomonal attractant for codling moth. Et-E,Z-DD appears to be chemically more stable than E,E-αF and can be loaded in septa to provide long-lasting, effective monitoring of adult populations (Light et al. 2001; Knight et al 2005). The potential effects of Et-E,Z-DD on oviposition of codling moth have not been reported. Herein, we report on the effects of Et-E,Z-DD on codling moth oviposition under laboratory conditions and evaluate its use as a lure to monitor egg laying in apple and walnut orchards.

MATERIALS AND METHODS

Choice and no-choice laboratory experiments. Moths 24-48 hr old were obtained from a laboratory colony reared on artificial diet (Toba and Howell 1991) at the U.S.D.A. Yakima Agricultural Research Laboratory in Wapato, WA. Individual virgin female moths were paired with two male moths for 24 h at 25 °C, > 40% R.H., and a 16:8 L:D photoperiod. Females were then placed in screened (3 x 3 mm) cylindrical cages (11 cm long and 9 cm diameter). Both ends of each cage were capped with a plastic cover lined with wax paper. Gray halobutyl elastomer septa (No. 1888, size No. 1,West Co., Phoenixville. PA) were pinned to the wax paper at each end of the cage. A 10.0% honey water wick was inserted into the middle of each cage.

Choice and no-choice tests were conducted with septa loaded with 1.0 and 100.0 µg Et-E,Z-DD (93.7% A.I., Trécé Inc., Adair, OK) versus septa treated only with the solvent, dichloromethane as a blank. In choice tests an Et-E,Z-DD-loaded septa and a solvent blank septa were pinned to the wax paper at opposite ends of the cage. Identical lures were pinned at each end of the cage in the no-choice tests. Tests were run for 96 h inside greenhouses maintained between 20 - 25 °C. Cages were spaced > 5 m apart and no more than four replicates were run on each of six dates. An additional no-choice test was conducted with 1.0 µg Et-E,Z-DD septa versus a solvent control septa using moths reared from an overwintering population collected as larvae the previous season in corrugated bands attached to apple trees. Larvae had been maintained under diapause conditions (2 °C and total darkness) for five months and were allowed to emerge in rooms maintained at 25 °C, 16:8 L:D and > 45% R.H. The numbers of eggs laid on each wax paper cap were counted in all experiments and females were dissected to determine their mating status. Only data from mated females were included in the statistical analyses (15 - 20 replicates per comparison).